1. Field of the Invention
The present invention relates to an insulated IC pressure sensor, particularly to an insulated IC pressure sensor using a pressure-sensitive integrated circuit (IC) as a pressure sensor for sensing pressure of an electrically conducting fluid.
2. Description of Related Art
Conventional pressure sensors for fluids are mercury pressure sensors or mechanical pressure sensors using springs. However, mechanical pressure sensors are voluminous and expensive and have bad reactivity and reactivity. Therefore, in recent years semiconductor pressure sensors have been developed.
A conventional semiconductor pressure sensor uses a pressure-sensitive integrated circuit (IC), comprising, as shown on FIG. 7, a base 1; an adapter 2 on an upper side of the base 1 for connecting to a pipe and letting in fluid; an electronic circuit board 3 on the upper side of the base 1; a pressure-sensing IC 4, having several feet soldered to the electronic circuit board 3; several wires 5, connected to the electronic circuit board 3 for transmitting pressure data to an external processing device; and a cover 6, placed on the upper side of the base 1 and protecting the electronic circuit board 3 and the pressure-sensing IC.
The pressure-sensing IC 4 has several pressure-sensitive resistors having electrical resistance values that vary with varying pressure.
A conventional semiconductor pressure sensor is directly contacted by fluid the pressure of which is to be sensed and hence suitable for measuring air pressure, but due to risk of short-circuits becomes ineffective if the fluid is electrically conducting.
Since electrically conducting fluid has to be kept insulated from the pressure-sensing IC, pressure-transmitting devices like pistons have been employed to measure pressure of electrically conducting fluid, like water or oil. As shown in FIG. 8, a case 7 is put over the base 1, housing a piston 8 with an outer side, against which fluid presses causing a movement of the piston 8. Air is used to transmit pressure from the piston 8 to the pressure-sensing IC 4, so that pressure of the fluid is sensed indirectly.
Damaging of the pressure-sensing IC 4 by electrically conducting fluid is thereby avoided, but the case 7 and the piston 8 lead to dissipation of mechanical energy, lack of sensing precision and, due to usage of transmitting compressed air, temperature dependence of sensed pressure values. Furthermore, friction of the movement of the piston 8 causes the piston 8 after a release of pressure to return to a position different from an original position, resulting in poor repeatability.
Therefore, direct sensing of fluid pressures is not possible in many cases, limiting the range of applications, and indirect sensing is imprecise.